Rebels from Uganda's Lord's Resistance army (LRA) have continued their rampage through central Africa, killing more than 50 civilians in south Sudan and Democratic Republic of Congo.

The attacks come after raids on Congolese villages that left up to 500 people dead in the days after Christmas. The rebels, forced from their hideouts in north-east Congo by a joint force comprising troops from Uganda, Sudan and Congo, are believed to be operating in small groups.

Most victims of the attacks, the bloodiest by the rebels in several years, had been hacked to death with machetes. More than 225 people, mostly children, were reported to have been kidnapped by LRA fighters. About 50,000 people fled their homes in Sudan and Congo, which both border Uganda.

Jemma Nunu Kumba, the governor of Western Equatoria state, in south Sudan, said the LRA had killed 38 people during the final week of 2008.

"They have caused unprecedented havoc ..." Kumba told Reuters. "We are now a target area. This is more than hunger. This is revenge."

Between last Friday and Sunday, rebel fighters killed 13 people in attacks on three villages in north-east Congo. A spokesman for the Congolese army said tracking the rebels, who are renowned for their bush skills, was difficult due to the lack of roads in the area. The worst attack occurred at Nagero, the headquarters of Garamba national park, where the LRA leader, Joseph Kony, was believed to be hiding. Among the eight victims were two park rangers and the wives of two wardens.

Kony, a self-proclaimed mystic, began his rebellion in northern Uganda against President Yoweri Museveni in the late 1980s, but soon turned on the local population. More than 20,000 people, mostly children, were kidnapped, becoming sex slaves, porters or fighters. At least 10,000 people died, while 1.6 million were forced into displacement camps.

Kony agreed to a ceasefire in 2006, which led to a lull in attacks for more than two years. But his refusal to sign a final peace deal – Kony claims that war crimes charges brought by the international criminal court against him and two other commanders are the final sticking point – prompted Uganda, Congo and Sudan to launch Operation Lightning Thunder in early December.

Analysts who warned that the approach would fail – like several previous attempts by Museveni to end the conflict by force – and instead provoke the rebels, have been proved correct. Chris Dolan, the director of the Refugee Law Project in Kampala, said: "It's hard to imagine that keeping the negotiating door open and prolonging what was a contained situation with little violence could be more expensive – in terms of dollars, human lives and impact on stability – than sending in the troops."